The present invention is generally directed to mechanisms for engaging electronic circuit modules with or in land grid array (LGA) socket devices. More particularly, the present invention is directed to a mechanism which reduces stress on electronic circuit components while at the same time provides access for direct lid or heat sink attachment. Even more particularly, the present invention is directed to land grid array socket mechanisms which apply a continuous yet distributed force for engagement, but which still permit easy removal of the electronic circuit component portion.
The land grid array interconnection system is one that is widely requested and is a highly desirable mechanism for engagement between electronic circuit components and underlying sockets for mechanical and electrical interconnection. However, land grid array interconnection mechanisms suffer from certain disadvantages. In particular, these mechanisms typically require relatively large compressive forces in order to maintain sufficient electrical contact throughout the card/socket/module system. Typically these forces are generated by clamping a bulky pressure plate which fits entirely over the top surface of the module assembly. This pressure plate is typically fastened to the card via screws. However, the compressive force generated by such a mechanism can impart large tensile, compressive and shear stresses on sensitive electrical components such as the silicon chip, the chip carrier (which is typically ceramic), the chip underfill material, lid adhesive and any thermal compound which may be disposed between the chip and an overlying lid. Accordingly, packaging structures employing direct lid attach (DLA) ceramic packaging are not particularly well suited for standard LGA interconnection mechanisms. However, it is nonetheless very desirable to be able to employ direct lid attach packaging.
Over time it is also possible that certain failures can occur in standard land grid array engagement mechanisms. In particular these include interface delamination, bulk material fracture and material creep. These stresses are predicted to cause some highly stressed modules to fail.
An added disadvantage to the standard pressure plate land grid array interconnection system is that it entirely covers the top surface of the module. Thus, thermal performance is significantly degraded due to the low thermal conductivity of the pressure plate which typically comprises a material such as steel which is provided for its strength. However, the thermal conductivity of steel is significantly less than the thermal conductivity of such materials as aluminum or copper. Additionally, the added thermal interface that exists between the pressure plate and the top surface of the module also acts to degrade thermal performance. Since the land grid array interconnection mechanism is largely targeted for leading edge and high performance, high thermal stress modules, this limitation in thermal performance is very desirable particularly in modules that generate significant amounts of heat.